c# - 选择 column='null' 的数据

Question

我想查询数据，并且列（大陆）的值为“非洲”或 Null。

我想在查询中使用此列名，但对于名称不是非洲的国家/地区，我没有得到任何数据。

这是我尝试过的，但没有返回任何数据。

SqlDataAdapter dba = new SqlDataAdapter(@"SELECT * from [tblCountries] 
                     WHERE [Continent] = '' order by [Common Name]", connection);
                    //WHERE [Continent]<>'Africa' order by [Common Name]", connection);
                   //WHERE [Continent] IS null order by [Common Name]", connection);
dba.Fill(ds);

drpNonAfricanCountries.DataSource = ds;

这样做的正确方法是什么？

Answer 1

我想查询数据，并且列（大陆）的值为“非洲”或 Null。

WHERE [Continent] = 'Africa' OR  [Continent] IS NULL

用于比较列与NULL使用IS NULL

所以你的最终代码应该是：

SqlDataAdapter dba = new SqlDataAdapter(@"SELECT * from [tblCountries] 
               WHERE [Continent] = 'Africa' OR  [Continent] IS NULL order by [Common Name]", connection);

Answer 2

像这样试试

SqlDataAdapter dba = new SqlDataAdapter(@"SELECT * from [tblCountries] 
                                     WHERE [Continent] IS NULL order by [Common Name]", connection);
            dba.Fill(ds);
            drpNonAfricanCountries.DataSource = ds;

Answer 3

select * from tblCountries where (Continent = 'Africa' or Continent is null)

Answer 4

尝试这个：

SELECT * from [tblCountries] WHERE [Continent] IS NULL OR [Continent]= 'Africa' order by [Common Name];